In automatic transmissions known from practical applications, which comprise friction-locking shift elements and form-locking shift elements for obtaining different gear ratios, the shift command for engaging a form-locking connection by applying force is triggered by a transmission control or transmission software implemented in the transmission control with a certain time delay before the synchronization point of the form-locking shift element is reached.
The time delay is influenced to a considerable extent by the operating temperature of the transmission oil, inter alia, in particular when the form-locking shift elements of automatic transmissions are hydraulically actuated.
The time delay that is required, in a particular case depending on the operating state, or the time period between the time of the shift request and the engagement time of the form-locking shift element, is preferably determined empirically and, during operation of an automatic transmission, is determined as a function of the gradient of a transmission input speed or an equivalent rotational speed parameter.
This approach should ensure that events which delay implementation of the shift command such as signal transit times, hydraulic delays, covering the distance to engage the form-locking connection, and the like, are taken into account to the extent that a rotational speed differential between the halves of the shift elements of the form-locking shift element to be engaged lies within a predefined rotational speed differential window at the engagement time, wherein all of the rotational speed differentials encompassed by the rotational speed differential window represent a precondition for comfortable engagement of the form-locking shift element.
Document DE 197 56 637 A1 makes known a shift device for connecting components of a transmission rotating at different speeds and at least one shift group, wherein the shift device is actuated by a control fluid. A unit containing valves, shift cylinder pistons, and shift elements is provided for each shift group of the transmission. Pulse-operated 2/2 directional control valves are used as the triggering valves. A position-measuring system is used to determine the actual position of the piston relative to the shift cylinder of a shift element. When gears are meshed to form a torque-transferring connection, the shift force and shifting time are adjusted in order to attain variable synchronization times and faster shifting times.
The above-described transmission devices have the problem, however, in that spontaneous changes in the gradient of the transmission input speed or the equivalent rotational speed parameter that results, for example, from a great change in the gas pedal position of a vehicle or strong braking of the vehicle by the driver cannot be taken into account to a desired extent after the time of the shift request to engage a form-locking shift element.
This is due to the fact that the gradient that exists at the time of the shift request no longer corresponds to the actual gradient, and the engagement time of the form-locking shift element determined at the time of the shift request across the selected time period no longer coincides with the point of time at which the rotational speed differential of the form-locking shift element lies within the rotational speed differential window required for comfortable engagement of the form-locking shift element. If the form-locking shift element is then engaged outside of the desired rotational speed differential window, shifting noises are produced that affect driving comfort, and torque reactions occur in the drive train, which can be perceived by a driver in the form of jerks.
DE 102 44 023 A1 shows such a method for operating a transmission device comprising a plurality of fiction-locking and form-locking shift elements for obtaining different gear ratios.